The history of the Porin Ässät starts in 1925, when Porin Palloilijat was established, even though PoPa is often considered as a separate club from Ässät.

In 1932, Porin Kärpät was established and six years later RU-38 started operations in sports. PoPa and Kärpät merged in 1960 to become the Porin Karhut. Only seven years after the establishment of Karhut, it merged with RU-38 to become Ässät.

Karhut won the Finnish Championship of ice hockey in 1965. RU-38 won it two years later in 1967. Ässät claims neither of said championships.

Ässät themselves have won three championships in ice hockey and one Finnish Cup.

1925–1967: Before the establishment

Ässät's history in ice hockey can be traced back to the 1950s, when Porin Kärpät played their first official match in the Maakuntasarja. Ässät's history in other sports can be traced back to 1925, when PoPa was established.

RU-38 was established in 1938 by Oy W. Rosenlew Ab.

In 1960, PoPa and Kärpät merged to form Porin Karhut. Both Kärpät and PoPa were re-established as independent clubs years after the merger. PoPa did not have any ice hockey programs and only played football and basketball. Kärpät also had bandy in its programme.

In the early 1960s, two clubs from Pori joined the SM-sarja: Karhut and RU-38. Both quickly rose to the top of the league and achieved success in the SM-sarja. Karhut won the Finnish championship in 1965, followed by RU-38 two years later in 1967. There was fierce competition between the two clubs both on and off the ice. The town was divided into the Karhut and RU-38 fan clubs; the Karhut were more popular because the majority of the people considered it the city's own club. The RU-38, on the other hand, was considered a Rosenlew factories-funded team, but it still had its own supporters. The relations between the clubs were not very good.

Establishment of Ässät (1967) Although the RU-38 won the Finnish championship in 1967, the Rosenlew company seriously considered giving up sports activities, as Rosenlew felt that hockey did not bring enough positive publicity to the company. The leaders of Karhut and RU-38 negotiated the unification of the clubs during the spring and early summer so secretly that even the insiders of the teams did not get to know about the merger negotiations. The problem for the Karhut was the economic downturn, as the club had heavily invested in player acquisitions. The income was not enough to cover the expenses, especially after some supporters had moved to the Rosenlew club.

As Rosenlew was abandoning the sports club, it was suggested that the RU-38 was simply "melted" into Karhut. When an agreement was finally reached, Rosenlew took over a large portion of Karhut's debts and promised to support the new team financially in the early years. The new club was named Porin Ässät. The birth of the club was announced at the end of June 1967. The name of the club was given by Vilho Santala, who acted as a negotiator in uniting the clubs and was elected the first chairman of Ässät. The club's logo was designed by Vesa Antikainen. The colors of the club were chosen as red, black and white.

In addition to hockey, the Ässät football team inherited RU-38's place in the Mestaruussarja, while Karhut continued to play as Ässät's secondary team until 1968. Ässät's football club was later disestablished in 1981.

1967–1970: First seasons

The early days of Ässät did not go smoothly, with Karhut and RU-38 players on the same team creating a heated atmosphere. The merger of the two top clubs also raised hopes of a very strong team, but one line of national team-level players joined different teams, and the players who left were mainly RU-38 players from the previous season. The first team of Ässät thus consisted mainly of Karhut players.

The first games of Ässät went well, and even before the start of the 1967 SM-sarja season, Ässät won the Suomen Cup championship. In the final match played in Savonlinna, SaPKo collapsed. Thanks to inheriting the RU-38 championship, Ässät also played in the 1968 European Cup, where it won its first two rounds before being beaten by SC Dynamo Berlin in the quarter-finals.

In its first season in the 1967–68 SM-sarja, Ässät placed fourth with Rauli Virtanen's coaching. The new club did not receive unreserved support from the people of Pori, as the number of spectators decreased by 10,000 from the last season of Karhut. In the second season of Ässät attendance started to rise, with the numbers rising to the same level as Karhut had. Lasse Heikkilä, the former coach of Karhut, became the coach for the second season and served as the team's coach until 1974 and later in 1976–1981. In the 1968–69 season, Ässät were again fourth. For the following season, 1969–70, Ässät suffered two heavy losses when Veli-Pekka Ketola and Alpo Suhonen left for Jokerit for a year. Ässät finished sixth in the series.

1970–1971: First national championship

For the season 1970–71, Ässät got a high-class returnee from Helsinki when Veli-Pekka Ketola returned to Pori after playing for one season in Jokerit. Alpo Suhonen also returned to Ässät after Ketola. Ketola's return to his home club gave rise to a huge training enthusiasm in other players as well, and coach Lasse Heikkilä took the team on a training trip to Moscow before the start of the season. The trip to the Soviet Union started training very early, by the standards of the time, because there was no ice on Pori in early autumn. In the 1970–71 season Ässät finished third in the regular season after Jokerit and HIFK. In the final series, everything fell into place, Ässät lost only one of their ten matches and overtook the Helsinki clubs ahead. The gold medals were finally secured by a five-point difference to the Jokerit who came in second. The first championship came under the leadership of the forward trio Erkki Väkiparta - Veli-Pekka Ketola - Tapio Koskinen. Other lines behind No. 1 were also able to provide to the team. There were also big names in the defense, such as Antti Heikkilä and Pekka Rautakallio. Veli-pekka Ketola was the highest point scorer in the SM-sarja during the 1970–71 season with 42 points, of which 25 were goals and 17 were assists. Ässät's captain during the season was Raimo Kilpiö. Ässät's number one goalie was Jorma Valtonen who played every game of the season. Valtonen finished the season with a .922 save percentage.

1971–1977

Not much was expected from Ässät in the following seasons. Ässät remained the same after the championship season and an arena was built in Pori, but no lasting success was achieved. In the four seasons following the championship season, the club placed in the middle caste of the series and did not seek medals, but there was no threat of relegation either.

Not was much expected for the 1975–76 season. The worst loss was Pekka Rautakallio's departure to North America. However, promising young people came to Ässät; Tapio Levo filled the gap left by Rautakallio. The net was blocked by the young Antero Kivelä. The young team of Ässät showed their potential in the series by beating the clubs that were predicted to be at top of the series. It was worst experienced by the future champion TPS, who Ässät beat 14–0. However, the access for Ässät to the top four in the playoffs was only decided in the final round against Lukko. In the semi-finals, Ässät challenged Tappara, who advanced to the finals 2–0. In the bronze matches against HIFK, Ässät's hunger for victory was greater and the team took the bronze winning the series 2–0.

At least as good a performance was expected for the following season, 1976–77, but Ässät remained fifth in the series and thus did not make the playoffs.

1977–1987: Medal streak and the downfall

Championship 1977–78 The 1977–78 season again raised hopes of success when Pekka Rautakallio and Veli-Pekka Ketola returned to Ässät from North America. In addition, promising young people played in the club, such as Arto Javanainen, Kari Makkonen, Tapio Levo and Harry Nikander. Ässät finished second in the regular season after Tappara and defeated TPS 3–2 in the semi-finals. The final series against Tappara did not start promisingly, as Tappara won the first match in Tampere 8–0. However, Ässät won the rest of the games, and the club achieved its second Finnish Championship. The last match at the Porin jäähalli (now Isomäki Areena) was estimated to have been attended by more than 13,000 spectators, even though only 8,600 spectators should have been allowed into the arena at that time. There were more spectators in the auditorium than in any other previous hockey match played in Finland. In the early years of the SM-liiga in the second half of the 1970s, Ässät was one of the league's absolute top teams. The most important player on the team was the captain, center Veli-Pekka Ketola, who had returned from the North American WHA League. Ketola broke the point record in the playoffs at the time.

Silver 1978–79 The season that followed the championship, 1978–79, went as expected for Ässät in the regular season. The team won it by five points to Tappara. In the semifinals, Ässät knocked out HIFK with a win of 3-0 and advanced to the final against Tappara. Last year's finalists struggled again for the championship. The final series became a thrilling play. Tappara won the first two matches, Ässät the next two and the final series thus stretched to the fifth, decisive match. The match played in Pori ended with Tappara's 2–5 victory, so Ässät was left with silver.

Silver 1979–80 In the following season, 1979–80, Ässät were nowhere near the previous season in the regular season, finishing fourth. In the semi-finals, TPS was defeated by Ässät 3–1, winning the finals for the third time in a row. HIFK came up against Ässät. HIFK took the championship 3–0, so Ässät were silver medallists again.

Silver 1983–84 After the silver seasons, Ässät suffered bad losses when Veli-Pekka Ketola went back to North America. Tapio Levo also joined the NHL. In addition, Risto Tuomi and Veli-Matti Ruisma went to the Swedish league and Erkki Väkiparta retired. In the following seasons, Ässät placed in the middle caste of the SM-Liiga. For the 1983–84 season, the team received well-known returnees when Tapio Levo returned from the NHL and Risto Tuomi and Harry Nikander from Sweden. The team was also strengthened by its own juniors, from whom more top players of the future were emerging; In addition to Javanainen and Levo, Kari Takko and Christian Ruuttu, among others. The team placed second in the regular season and beat Oulun Kärpät 3–2 in the semi-finals. In the finals, the opponent was again Tappara. The series was close. Ässät won the first match in overtime but Tappara took the next three. The overtime goal of the decisive match secured Tappara the championship with 3–1 victories.

1984–1987 In the following season, 1984–85, Ässät survived to the medal games, but still finished fourth. In the next three seasons, 1985–88, the team's success slowed down and Ässät were placed in the middle caste of the SM-liiga. However, access to the top four playoffs was only a few points away each time, so there was no threat of relegation. Ässät also saw the first foreigner in the 1986–87 season, when a Canadian Mark Jooris played in Pori for two seasons.

1988–1990: New momentum from Division 1